MdTable

MdTable(T, Rows, Cols,Vars, conglomerationFn, defaultValue, valueColumn)

In the default case, it converts a 2D relational table, «T», indexed by «Rows» and «Cols», into an N-dimensional array result. Given M = Size(«Cols»), N = M - 1.

Each cell in thee result is the sum over the values in the last column of «T» for all rows whose coordinates correspond to the index values of the result. All except the last column in «Cols» of «T» are interpreted as coordinates. «Vars» should be a list of identifiers of (as text) or handles to the Indexes to be used in the result.

MdTable is analogous to PivotTable in Excel. It is the inverse of MdArrayToTable().

This default behavior can be modified by a number of optional parameters.

MdTable interprets the first N columns (along the «Cols» index) as containing a coordinate in the final multi-dimensional array, and last remaining M columns as containing values (in OLAP terminology, measures), where N + M = Size(Cols). In the most common usage, M = 1 and N = Size(«Cols» - 1), meaning that all columns except the last specify the coordinate, and the last column contains the cell value. In this case, the «Vars» and «valueColumn» parameters are optional. If the «Vars» parameter is specified, its length determines how many columns are used for coordinates, and if its length is less than Size(«Cols»)-1, then the «valueColumn» parameter must be specified to indicate which column contains the cell value.

Before using MdTable, you must define all of the indexes for the result. Each index must include all values that occur in the corresponding column of «T» or an error will result. The Unique() function is useful for defining the necessary indexes.

Optional parameters

Vars

Must be a list of identifiers of (as text) or handles to Indexes or index names. If an element is a text identifier, it must refer to a global index -- i.e,. not a local index). If it is a handle, it can refer to a local index. If you don't specify optional parameter «Vars», MdTable() assumes that the first Size(«Cols») - 1 elements of the «Cols» index are identifiers of Global indexes to be used in the result. You must make sure that all these Indexes have as values all the unique values from the corresponding column in «T», for example:

Index Cols := ['A', 'B', 'Value']

Index Rows := 1..100

Variable T := Table(Cols, Rows)(.....)

Index A := T[Cols = 'A', Rows = Unique(T[Cols = 'A'], Rows)]

Index B := T[Cols = 'B', Rows = Unique(T[Cols = 'B'], Rows)]

Variable Result := MDArray(T, Rows, Cols)

conglomerationFn

It is possible that two or more rows of «T» specify identical coordinates. In this case, a conglomeration function is used combine the values for the given cell. The «conglomerationFn» parameter is a text value specifying which conglomeration function is to be used. Some possible values are: "sum" (default), "min", "max", "average", or "count" or "product".

But you can specify the identifier (as text) of any reducing function that operates over an index, with parameters of the form: (A: Array[I]; I: Index). It is OK if it has other parameters as long as they are optional.

You can also create your own custom conglomeration function as a UDF.

defaultVal

(Default: NULL) The value of a result cell that has no corresponding rows in «T». It is often a good idea to set the default to 0.

valueColumn

In OLAP terminology, a fact table is a table in which the first N columns specify coordinates in a multi-dimensional cube, and the last M columns specify measures along a measure dimension, so that the final multi-dimensional array has N + 1 dimensions, the extra dimension being the measure dimension. This transformation is accomplished by providing the measure dimension in the «valueColumn» parameter. The «valueColumn» parameter should then be a 1-D array, indexed by your measure dimension, where the array elements identify columns in the «Cols» index. An index with n values equal to the last n values of «Cols». In this case, Vars should identify as indexes only the first m-n elements of «Cols» -- where m = Size(«Cols»). The remaining «Cols» are mapped into «valueColumn». The result will also be indexed by «valueColumn» if specified, and each slice in the result contains the values aggregated over the corresponding Col in «T». In OLAP terminology, parameter «T» a "Fact table", which shows more than one value for each combination of «Vars».

Library

Array

Examples

Download model with examples

Suppose T, Rows, and Cols are defined as indicated by the following table:

	Cols ▶
Rows ▼	Car_type	Mpg	X
1	VW	26	2185
2	VW	30	1705
3	Honda	26	2330
4	Honda	35	2210
5	BMW	30	2955
6	BMW	35	2800
7	BMW	35	2870

MDTable(T, Rows, Cols, [Car_type, Mpg], 'average', 'n/a') →

	Mpg ▶
Car_type ▼	26	30	35
VW	2185	1705	n/a
Honda	2330	n/a	2210
BMW	n/a	2955	2835

Notice that in the example, Rows 6 and 7 both specified values for Car_type = BMW, Mpg = 35. The "average" conglomeration function was used to combine these.

Now suppose we have a User-Defined Function, First:

Function First( A : Array[I] ; I : Index ) := A[@I = 1]

Then

MdTable(T, Rows, Cols, [Car_type, Mpg], 'First', 'n/a') →

	Mpg ▶
Car_type ▼	26	30	35
VW	2185	1705	n/a
Honda	2330	n/a	2210
BMW	n/a	2955	2800

To aggregate X over Car_type, we can use the «valueColumn». Here we will aggregate using Sum.

MdTable(T, Rows, Cols, [Car_type], valueColumn: 'X') →

Car_Type ▼
VW	3890
Honda	4540
BMW	8625

In the previous example, Car_type is the first column. When you aggregate in this fashion, the target aggregation index must be the first column. If you wanted to aggregate onto Mpg (summing all records with the same Mpg) then you would need to re-index first to make Mpg the first column like this:

Index L := ['Mpg', 'X'];

MdTable(T[Cols = L], Rows, L, [mpg], valueColumn: 'X') →

Mpg ▼
26	4515
30	4660
35	7880

If T had 6 coordinate columns and you wanted to aggregate onto 3 dimensions only, then you'd need to make sure that the three final dimensions were in the first three columns. If they were not there initially, then you'd reindex as in the previous example. If you are aggregating only a single target dimension, the Aggregate function can also be used and may be more intuitive. MdTable is actually more general since you can aggregate onto a multi-dimensional table.

To use both Mpg and X as value columns, we can define a measure dimension:

Index Measure_Index := ['Mpg', 'X']

Then

MdTable(T, Rows, Cols, [Car_type], valueColumn: Measure_Index) →

	MeasureIndex ▶
Car_Type ▼	Mpg	X
VW	56	3890
Honda	61	4540
BMW	100	8625

Notice here that both Mpg and X have been summed -- both values used the same conglomeration function. However, suppose we want the average value for Mpg, but the maximum value for X, i.e., each "measure" having its own conglomeration. We can accomplish this using:

MdTable(T, Rows, Cols, [Car_type], valueColumn: Measure_Index,

conglomerationFn: Array(Measure_Index, ["average", "max"])) →

	MeasureIndex ▶
Car_Type ▼	Mpg	X
VW	28	2185
Honda	30.5	2330
BMW	33.3	2955

Fact Table

In order to convert a 2D relational table with more than one value per combination of indexes, you would use the parameter «valueColumn» to create a Fact Table. For example, suppose T, Rows, and Cols are defined as indicated by the following table:

	Cols ▶
Rows ▼	Car_type	Mpg	X	Y
1	VW	26	2185	1
2	VW	30	1705	2
3	Honda	26	2330	3
4	Honda	35	2210	3
5	BMW	30	2955	4
6	BMW	35	2800	5
7	BMW	35	2870	5

And suppose Fact is an index defined as ['X', 'Y']. Therefore:

MDTable(T, Rows, Cols, [Car_type, Mpg], valueColumn: Fact, defaultValue: "n/a") →

MPG = 26	MPG = 30	MPG = 35
Fact ▶ Car_type ▼ X Y VW 2185 1 Honda 2330 3 BMW n/a n/a	Fact ▶ Car_type ▼ X Y VW 1705 2 Honda n/a n/a BMW 1955 4	Fact ▶ Car_type ▼ X Y VW n/a n/a Honda 2210 3 BMW 5670 10

Notice that in the example, Rows 6 and 7 both specified values for Car_type = BMW, Mpg=35. By default the Sum conglomeration function was used to combine these.

History

Introduced in Analytica 4.0.

See Also

• Unique
• MdArrayToTable